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The present invention relates to a resin composition with superior antioxidant properties, as well as mechanical strength and insulating properties.
The present inventors proposed a certain type of resin composition in Japanese Unexamined Patent Application Disclosure (Kokai) No. 10-87840. There, a thermoplastic resin was wetted in water with an oxidation-reduction potential of between xe2x88x92420 mV and 200 mV and the wet thermoplastic resin was melted under heat and pressure to form an antioxidizing resin. The thermoplastic resin was melted at a temperature between 170xc2x0 C. and 250xc2x0 C. under pressure ranging between 5 and 30 MPa. Low molecular antioxidant substances produced by a group of effective microorganisms were mixed in with the xe2x88x92420 mV to 200 mV water.
This antioxidizing resin is ideal in film for wrapping food products and containers for storing food products because of the good oxidation-inhibiting effect of the resin on vegetables, fruits, grains, meats and fish. However, when this resin was used for large containers, such as containers used for transporting food products or tanks for storing drinking water, the resin maintained its superior antioxidizing properties but did not exhibit sufficient mechanical strength for manufacturing large containers.
An object of the present invention is to obtain a resin composition with superior antioxidant properties, mechanical strength and insulating properties.
According to one embodiment of the present invention, the thermoplastic resin of the present invention is formed by melting a mixture of a thermoplastic resin in pellet or granular form and purified water or distilled water with the impurities removed. The melting is performed by using heat and pressure under a subcritical condition of water. The melted resin is then cooled by, for example, using cold water with the impurities removed.
According to another embodiment of the present invention, the thermoplastic resin of the present invention is formed by melting a mixture of a thermoplastic resin in pellet or granular form and natural unchanged water. The melting is performed by using heat and pressure under a subcritical condition of water. The melted resin is then cooled by, for example, using cold water with the impurities removed.
According to a further embodiment of the present invention, the thermoplastic resin of the present invention is formed by melting a mixture of a thermoplastic resin in pellet or granular form and purified water or distilled water containing antioxidizing substances produced by groups of effective microorganisms. The melting is performed by using heat and pressure under a subcritical condition of water. The melted resin is then cooled by, for example, using cold water with the impurities removed.
Preferably, the thermoplastic resin is polyethylene or polypropylene; however, the present invention is not restricted to these two types of resin.
One method for manufacturing a resin composition of the present invention comprises a first stage wherein a thermoplastic resin in pellet or granular form is mixed and stirred in purified water or distilled water with the impurities removed; a second stage wherein the mixture is heated and pressurized under a subcritical condition of water and the thermoplastic resin is melted; and a third stage wherein the melted resin obtained in the second stage is cooled using cold water with the impurities removed.
Alternatively, in the first stage, the thermoplastic resin in pellet or granular form may be mixed and stirred in natural unchanged water, or in purified water, or distilled water containing antioxidizing substances produced by groups of effective microorganisms.
The purified water with impurities removed refers to tap water filtered using ceramics, activated charcoal or any other means known in the art to remove impurities such as chlorine. The distilled water refers to tap water distilled to remove impurities such as chlorine. The natural unchanged water refers to water containing minerals such as, for example, deep ocean water, mineral water and anionic mineral water. The purified or distilled water containing antioxidizing substances produced by groups of effective microorganisms refers to purified water or distilled water containing a small amount of antioxidizing substances. Preferably, it is a mix of a small amount of antioxidizing substances produced by groups of effective microorganisms (1 to 5 ppw antioxidizing substances per 100 ppw purified water) and tap water dechlorinated using ceramics.
Preferably, the thermoplastic resin raw material is polyolefin resin such as, for example, polyethylene or polypropylene. However, the present invention is not restricted to these two types of resin. Other examples include polystyrene (PS), AS resin, ABS resin, methacrylic resin (PMMA), polyamide (PA), polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), ionomer (IO), polyvinyl butyral (PVB), polyvinyl alcohol (PVA), polyacetal (POM), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), fluorine-based resins (PFA, ETFE, etc.), polyimide (PI), polyarylate (PAR), polysulfone (PSU), polyether sulfone (PES), polyether imide (PEI), polyimide (PAI), polyurethane (PU) and cellulose-based resins such as acetyl cellulose and cellulose acetate butylate.
The resin pellets are melted by heat and pressure under a subcritical condition of water. Subcritical conditions of water refers to a state below the critical point of water (374xc2x0 C. and 22 MPa). The melting conditions depend on the type of thermoplastic resin, but in general, when an extruder is used, the thermoplastic resins may be melted under a pressure range of between 10 and 22 MPa (preferably between 15 and 22 MPa) and at a temperature range of between 150 and 370xc2x0 C. (preferably between 200 and 250xc2x0 C.).
Groups of effective microorganisms that produce antioxidizing substances are generally a group of more than 80 species of microorganism in 10 genuses of diffferent functions, which are known as xe2x80x9ceffective microorganisms (EM)xe2x80x9d. The principal types of bacteria are photosynthetic bacteria, lactic acid bacteria, yeasts and mycobacteria. (See Akio Hiyoshi, xe2x80x9cThe EM Encyclopedia: How the EM Environmental Revolution Will Change Human Lifexe2x80x9d, Sogo Unicom Co., Ltd., No. 282, p. 283.) The low molecular antioxidizing substances produced by EM are known as xe2x80x9cEM-Xxe2x80x9d. The EM-X are manufactured by fermenting plant material or seaweed using EM, removing the oxides using ozone, and removing the residues and microorganisms using various filters. EM-X comprises many different kinds of plant-derived or microorganism-derived antioxidizing substances.
The preferred ratio of mixing the thermoplastic resin in pellet or grain form (hereinafter referred to as resin pellets) and water is 1 to 5 ppw water per 100 ppw resin pellets. If less than 1 ppw or more than 5 ppw water is added, a resin composition with superior antioxidizing properties cannot be obtained.
It is clear from the physical property testing to be explained below that the resin compositions of the present invention have superior mechanical strength and insulating properties, and it is clear from the test data in the embodiment to be described below that the resin compositions of the present invention prevent oxidation. It is believed that melting the resin pellets at a subcritical condition of water improves the hydrophobic properties of the resin compositions (Physical Property Test No. 2), but the theoretical mechanism is not understood.
The present inventors were able to verify that the physical properties of the resin compositions in the present invention were not changed by the heat and pressure that are present during usual product molding processes. In other words, the physical properties of the resin compositions in the present invention were not changed when the pellets were molded (e.g., propylene melted at 200xc2x0 C.) and processed into containers or wrapping for food products.
Therefore, using the resin compositions of the present invention as molding material for containers and sheets prevents putrefaction or denaturing of the contents of the containers and allows the container to withstand heavy loads. For example, containers molded from the resin compositions of the present invention preserve fresh foods much longer than containers made from conventional resin compositions. Also, large containers for transporting foods and tanks for drinking water could also be molded using the resin compositions of the present invention, unlike the previous resin compositions. The resin composition of the present invention also can be used as a liner of a refrigerator, so that the refrigerator has a superior ability to keep fresh foods from spoiling. Because of improved mechanical strength, the resin compositions of the present invention can be used in situations requiring long-term use, such as liners for pipes. Because of improved electrical resistance and insulation breakdown strength, the resin compositions of the present invention also can be used to coat electric wires. If the resin compositions are made using non-chlorine resins such as polyethylene and polypropylene, development of dioxins can be prevented at the time of waste disposal.